Physics MCQ Quiz - Objective Question with Answer for Physics - Download Free PDF

The Correct answer is Equal to its weight.

Explanation:

• The buoyant force acting on an object is equal to the weight of the fluid displaced by the object. In this case, the object is floating, so the buoyant force is equal to the weight of the object.
• The buoyant force is caused by the pressure difference between the top and bottom of the object. The pressure is greater at the bottom of the object because the fluid is denser at the bottom. This pressure difference creates a force that pushes the object upward.
• When the buoyant force is greater than the weight of the object, the object floats. If the buoyant force is less than the weight of the object, the object will sink. If the buoyant force is equal to the weight of the object, the object will rise to the surface of the liquid.

So, the buoyant force acting on an object that floats in a liquid with half of its volume submerged in the liquid is equal to its weight.

Important Points

• When the buoyant force of liquid is less than the weight of the object, the object will be submerged or sank.
• When the buoyant force of the liquid is greater than the weight of the object, the object will float on the surface of the liquid. 
• NOTES: Buoyancy is the tendency of a liquid to exert an upward force on an object immersed in it.
• The buoyancy of a liquid depends upon the density of the fluid and the volume of the object immersed in the liquid.
• Thus we can say the buoyant force is greater if the volume of an object submerged in a liquid is Larger.

The Correct Answer is Option 4 i.e At topmost position.

Key Points

• When an object (ball) is thrown upwards its velocity will decrease as it goes upward due to deceleration by gravity.
• So its kinetic energy will decrease as it moves upward. But its potential energy will increase as it moves upward.
• Kinetic energy is zero and potential energy is maximum when the object reaches the topmost point.
• Kinetic energy is maximum just before striking the ground.

The correct answer is Both electrons and holes.

Key Points

• Semiconductors are materials that have a conductivity between conductors (generally metals) and nonconductors or insulators (such as most ceramics).
• At room temperature, a semiconductor has enough free electrons to allow it to conduct current.
• At or close to absolute zero a semiconductor behaves like an insulator.
• The cause of electrical conduction in semiconductors is due to the movement of the holes in the valence band and the movement of the electrons in the conduction band.
• Conduction occurs at a higher temperatures because the electrons surrounding the semiconductor atoms can break away from their covalent bond and move freely about the lattice.
• Holes are formed when the electrons from the outermost shell of the atom that is completely filled with the electrons move out to the conduction band.
• When the electric field is applied then as a result the electrons will start moving in the conduction band in the direction opposite to that of the electric field.

The Correct Answer is Ampere (A).

Key Points

• Coulomb Per Second (C/s) is a unit in the category of Electric current.
• It is also known as coulombs per second, (coulomb/second).
• This unit is commonly used in the SI unit system.
• Coulomb Per Second (C/s) has a dimension of I where I is electric current.
• 1 coulomb of charge flows through any cross-section of a conductor in 1 second, the electric current through it is said to be 1 ampere.
• The SI unit of current is coulomb per second, generally known as ampere.

Additional Information

Second-

• The second (s or sec) is the International System of Units (SI) unit of time measurement.
• It is the time required for an electromagnetic (EM) field to propagate 299,792,458 meters (2.99792458 x 10⁸ m) through a vacuum.
• This figure is sometimes rounded to 3 x 10⁸ m, or 300,000 kilometers (3 x 10⁵ km).
• One second is equal to 1/86,400 of a mean solar day.
• This is easy to derive from the fact that there are 60 seconds in a minute, 60 minutes in an hour and 24 hours in a mean solar day.

Joule-

• It is equal to the amount of work done when a force of one newton displaces a mass through a distance of one metre in the direction of that force.
• It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second.

Volt-

• Unit of electrical potential, potential difference and electromotive force in the metre–kilogram–second system (SI).
• It is equal to the difference in potential between two points in a conductor carrying one-ampere current when the power dissipated between the points is one watt.

The correct answer is Negative charge.

• A plastic scale after being rubbed against dry hair attracts bits of paper as it acquires a negative charge.
• The plastic scale gets electrically charged due to rubbing against dry hair.
• The plastic scale acquires charge due to static electricity.
• A temporary collection of charges will form near the rubbed surface of the plastic scale.
• The bits of paper are electrically neutral.
• Within the paper bits, the electrons get either attracted or repelled based on the charge of the plastic scale.
• The electrically charged scale exerts an electric force against the paper bits and attracts them.
• When a plastic scale is rubbed against dry hair, the material that has a stronger affinity for electrons pulls them from the other material.
  • A negative charge will produce on the material that has gained electrons.
  • A net positive charge will produce on the material that has lost electrons.

CONCEPT:

• Wave: The disturbance that transfers energy from one place to another is called a wave.

There are mainly two types of waves:

1. Transverse waves: The wave in which the movement of the particles is at right angles to the motion of the energy is called a transverse wave. Light is an example of a transverse wave.
2. Longitudinal wave: The wave in which the movement of the particles is parallel to the motion of the energy is called a longitudinal wave. The sound wave is an example of a longitudinal wave.

EXPLANATION:

• Light-wave is a transverse wave because its components vibrate perpendicular to its direction of propagation. So option 1 is correct.

The correct answer is Newton's first law.

Key Points

• Newton's laws of motion-
  • ​Newton’s first law states that, if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by force.
    • This postulate is known as the law of inertia. The law of inertia was first formulated by Galileo Galilei for horizontal motion on Earth and was later generalized by René Descartes.
    • Before Galileo, it had been thought that all horizontal motion required a direct cause. Still, Galileo deduced from his experiments that a body in motion would remain in motion unless a force (such as friction) caused it to come to rest.
  • Newton’s second law is a quantitative description of the changes that a force can produce in a body's motion.
    • It states that the time rate of change of a body's momentum is equal in both magnitude and direction to the force imposed on it.
    • The momentum of a body is equal to the product of its mass and its velocity. Momentum, like velocity, is a vector quantity, having both magnitude and direction.
    • A force applied to a body can change the magnitude of the momentum, direction, or both.
    • For a body whose mass m is constant, it can be written in F = ma, where F (force) and an (acceleration) are vector quantities.
    • If a body has a net force acting on it, it is accelerated by the equation. Conversely, if a body is not accelerated, there is no net force acting on it.
  • Newton’s third law states that when two bodies interact, they apply forces to one another that are equal in magnitude and opposite in direction.
  • The third law is also known as the law of action and reaction. This law is important in analyzing static equilibrium problems, where all forces are balanced, but it also applies to bodies in uniform or accelerated motion.
  • The forces it describes are real ones, not mere bookkeeping devices. For example, a book resting on a table applies a downward force equal to its weight on the table.
  • According to the third law, the table applies an equal and opposite force to the book. This force occurs because the book's weight causes the table to deform slightly so that it pushes back on the book like a coiled spring.

The correct answer is At the centre of the Earth.

• The centre of the Earth is such that if we are at that place, the mass around us can be considered to be condensed at the surface of the Earth itself, i.e considering the Earth as a spherical shell.
• Inside a spherical shell, there is no change in potential as one moves inside, and since only a change in potential implies a force there is no force.
• Hence the acceleration due to gravity is zero at the centre of the Earth.

The correct answer is Gamma Rays.

Key Points

• Gamma rays have the shortest wavelength and highest frequency (energy) in the electromagnetic spectrum.
• They are electromagnetic waves with wavelengths in the range of 10^-12m and frequencies around 10²⁰- 10²⁴ Hz.
• They have a high penetrating power.
• They are a result of decaying radioactive material and can also be found in outer space.
• They are used in medical applications for sterilisation of equipment and cancer treatment.

Additional Information

•  Other radiations in the Electromagnetic spectrum are:

The correct answer is 342 m.

CONCEPT:

• Echo: If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later. This sound which we hear is called an echo.
  • Echoes are heard due to the phenomenon of Reflection of sound waves.
  • To hear the echo clearly, the reflecting object must be more than 17.2 m from the sound source for the echo to be heard by a person standing at the source.

CALCULATION:

Speed of sound = 342 m/s.

The time is taken for hearing an echo = 2s.​

• The speed of sound is

\(⇒ Speed (v)= \frac{distance (d)}{time (t)}\)

Distance travelled = 2d = v × t

⇒ 2 × d = 342 × 2

⇒ d = (342 × 2)/2

The correct answer is the Microwave.

Key Points

• A microwave oven uses microwaves to heat food.
• In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500 megahertz (2.5 gigahertz).
• Radio waves in this frequency range absorbed by water, fats, and sugars. When they are absorbed they are converted directly into atomic motion or vibration.
• Therefore heavy motion or vibration is converted into heat.

Important Points

• Microwaves are not absorbed by most plastics, glass, or ceramics.
• The frequency of the Microwave equals the resonance frequency of water. Therefore foods could be heated up by the oscillation of water molecules.

Additional Information

• An Electric heater, Electric blub (with filament), Electric iron is the electrical device that converts an electric current into heat.
• They working on the principle of the Joule heating effect.
  • An electric current passing through a resistor will convert that electrical energy into heat energy.

The correct answer is 12250 W.

Concept:

• Power: Power is the amount of energy transferred or converted per unit time.
  • The unit of power is watt or J/s.
  • Its dimensional formula is: [M L² T^-3].

Calculation:

Given: v = 700 m/s, m = 50 g = 0.05 kg, n/t = 60 bullets/min ⇒  1 bullet/s

The power developed by the gun is given by formula -

Power = Work done / time = Energy consumed / time

\(Power = n \times \frac{{\frac{1}{2}m{v^2}}}{t}\)

\(Power = \frac{n}{t}\; \times \frac{1}{2}m{v^2}\)

\(Power = 1 \times \frac{1}{2} \times 0.05 \times {700^2}\)

Power = 12250 watt

Calculations:

Given,

Distance of the object from the lens = u = -10 cm

Refractive index of the lens = µ = 1.5

The Radii of curvature of the lens are 20 cm in magnitude

R₁ = 20 cm and R₂ = -20 cm          (As per sign convention)

According to Len's Maker's formula

\(\frac{1}{f}=(\mu - 1)(\frac{1}{R_1}-\frac{1}{R_2})=(1.5-1)(\frac{1}{20}-\frac{1}{-20})\\ =0.5 \times \frac{2}{20}=\frac{1}{20}\\ or, \; f=20 \; cm \)

From the Lens equation,

\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\\ \frac{1}{v}=\frac{1}{f}+\frac{1}{u}\\ or, \; v=\frac{fu}{u+f}=\frac{20 \times (-10)}{-10+20}=\frac{-200}{10}=-20 \; cm\)

The image is formed 20 cm on the same side as the object.

The correct answer is 10-4 microns.

Key Points

Read the question ,it is asking value  in microns not meter.

If asked in meters then the value will be 1 Angstroms  = 10^-10 m.

But asked in microns

• 1 mm = 10^-3 m
• 1 micron = 10^-3 mm
  • ⇒ 1 micron = 10-6 m
• 1 Angstrom = 10^-10 m
  • 1 Angstrom = 10-10 m = 10-10 × 106 micron = 10-4 micron.

Confusion Points

1 Angstrom = 10^-10 meter

1 Angstrom =  10^-4 micron

Additional Information

• An Angstrom is a unit of length used to measure very small distances.
• 1 Angstroms to = 0.0001 Microns 
• It is named after Anders Jonas Ångström (Swedish physicist).
• A micron is one-millionth of a meter (10−6 m) and one Angstrom is 10-4 micron.

The correct answer is Ohm.

Key Points

• Impedance is the total sum of resistance and reactance.
• The SI Unit of Impedance(Z), resistance(R), and reactance(X) is Ohm(Ω).
• Reactance is a kind of imaginary resistance offered by electrical components like Capacitance and Inductor.
  • Reactance offered by the Inductor is called Inductive reactance, given as X_L = 2πfL.
  • Reactance offered by the Capacitor is called Capacitor reactance, given as  \(X_{C}=\frac{1}{2\pi fC}\).
  • Where 'f' - frequency of the source, 'L' - Inductance, and 'C' - Capacitance.

Additional Information